Method and apparatus for automatically defrosting evaporators



May 29, 1951 T. L. WARREN -2,554,848

METHOD AND APPARATUS FOR AUTOMATICALLY DEF'ROSTING EVAPORATORS ANU-FREEZE y INVENTOR. W10/nas Warren @WM/g. v

May 29, 1951 T. WARREN METHOD AND APPARATUS FOR AuToMATIcALLY DEFRos'rING EvAPoRAToRs 2 Sheets-Sheet 2 Filed Feb. 6, 1948 JNVENTOJL 7710/170: Lf Warren ATTORNEYS Patented May 29, 1951 D UNITED STATES OFFICE METHOD AND APPARATUS FORAUTOMATI- CALLY DEFROSTING EVAPORATORS l Claims.

This invention relates to improvementsin a method and an apparatus fordefrosting .an evaporator; and relates more particularly to a method and an apparatus `for automatically defrosting one or more low temperature. evaporators such as are used for preserving frozen food products requiring the maintenance of relatively low tem,- peratures. It will be understood that while the present invention may be applied to commercial types of refrigerators, it may also be applied to smaller size domestic refrigerators or to .anylow temperature evaporator requiring a -quick .de-` frost regardless of the particular applicationrof the evaporator.

In the preservation of frozen food products at low temperature (10 F. or less), it is desirable for efficient operation to provide a rapid defrost of the evaporator coil at frequent intervals to remove the ice from the coil Without an lex cessive rise in the refrigerator temperature. Several methods have lheen used to accomplish this result. In one of these methodshot refrlg erant gas from the discharge side of the 'come pressor is pumped through the evaporatorv coil during the defrost cycle. y Such a system meltsl the ice from the inside and provides a quick defrost Without rliberating an excessive amount of heat in the refrigerator, but the defrosting capacity of such a system is limited by the amount of hotgas that can .be supplied' by the compressor of the particular condensing unit .and this system also causes an accumulation of lidud refrigerant in the evaporator coil which canpass back to the compressor unless an accumulator or heat exchange unit is used. Furthermore, such a system requires a connection to theidis,d charge side of the compressor which ynecesjsi-tatesz the removal of the holding charge of :refriger,- ant with which mostcondensing units are pro vided. Also, if the. refrigerating. cycle .and the defrost cycle in such asystem are automatie. callycontrol-led by a timing devicesetpfor den. nite intervals of time, there will be la :time lag that will shorten the defrost cycle vif ther refrigerator is down to temperature Whenthe de-..

frost cycle starts as the condensing-unit will not bein operation. Y 'Y Y The `present invention isv directed to providing a simplied apparatus and method for automaticontrol equipment andtheV defrosting operation is. carried out independently of the condensing unit. The present. inventionalso provides a` de* frosting method and @apparatus in which the del frostingcapacity, the length of the refrigeratng cycle and they-defrost cycle,.and the rate of defrosting can each he adjusted as desired in accordance with the requirements for a particular refrigerator.

The .foregoing and other objects and advantagesof the presentinventionwill be best under*- stood-from-the following description and the laccompanying. drawings in which:

Fig. 1 is a schematic view illustrating a re-4 frigerating -unit with a defrosting system embodying the present invention;

Fig. 2f-is a schematic wiring diagram for a ref-rigerating unitwith a de'irosting unit embody' ing the present invention;

Fig. 3 is a section view'of a refrigerator with' the Connections@ a defrosting unit embodying the inventionb'e'ing shown diagrammatically;

Fig. .el isa side' view in partial `section illus? dating a Cooling AinVaccordance with thermvention; and

Fig. 5is a section view'of the `evaporator nous. lllg showing the defrosting coil located therein.

Referring to thedrawi'ngs in detail, there isa refrigerator which basa cabinet or box L0. A cooling unit ha 'ng an evaporator coil H is enclosed in ollQHS-Ilgr I2i that is :located Within the cabinet Utes Figs- 3 .and 4. A circulating: fau liis secured to the housing l2 .tocirculatefthc air in thehox. over the evaporator coil; inl'. Theevaporator coil ilfisconnected. to acondensing unitfof Ithe.usualty-pe .(not shovvn.)v through.- a supply'line'V t4 andA aA suction line l5 and `the fii'ovv` yof "liquid refrigerant tov the evaporator coil mayV he controlled by a thermostaticvexpansionvalve -I6Lof the type shown and described-in application Serial-No. 538,574, --l'ed June 3, 1941i, now Patent No. `2-,475',f556, issued Jly'i; 13949.; Isolenoidcontrolled valve Il'l-v is located in the refrigerant supply line i4 and a 3 throttling valve I8 is located in the suction line I5.

A separate unit or chamber I9 for effecting defrosting of the evaporator coil and other parts of the cooling unit on which ice may collect is located outside of the refrigerator cabinet I0. The unit |9 consists of an insulated tank 20 containing a xed quantity of liquid 2| such as a permanent type, anti-freeze solution that is capable of being heated and storing heat Without materially changing the quantity of the liquid due to such heating. A heat exchange coil 22 is submerged in the liquid 2| and a low-wattage, immersion type electric heater 23 and an adjustable, differential thermostat 24 are also located in the liquid 2|. The thermostat 24 may be of the remote bulb type with its bulb immersed in the liquid 2|. A baflle plate 25 located between the heater 23 and the heat exchanger may also be provided in the tank 20 so as to cause circulation of the liquid 2| as it is being heated. The size of the tank 29 and the quantity of the liquid 2| will depend upon the size and type of the refrigerator and the quantity of the liquid 2| provided will have sucient heat storing capacity to accomplish the defrosting of the evaporator under maximum load conditions.

The high side of the heat exchanger 22 is connected to the evaporator through a line 26 and the suction line I5. The low side of the heat exchanger 22 is connected to the evaporator |I by lines 21 and 28 and through a solenoid controlled valve 29 and a collector 30 in the line 28. The low side of the heat exchanger 22 is also connected to the suction line I through the line 21, a line 3|, a defrosting coil 32 and a line 33.

As shown in Figs. Bland 4, the defrosting coil 32 is located on the under side of a false drain pan 34 that is supported in inclined position in the bottom of the housing I2 beneath the evaporator coil II. The false drain pan 34 has a drain 35 that extends into a water drain 36 for the housing I2 and the line 3| connecting the coil 32 to the heat exchanger also extends through the water drain 36.

As shown in the Wiring diagram, Fig. 2, the low-Wattage heater 23 is connected to a source of electrical energy S through a rheostat 31, a manually operable switch 38 and the differential thermostat 24. The connections of the heater 23 to the thermostat 24 are made so that during the refrigerating cycle the circuit to the heater is closed by the thermostat. Circuits connecting the fan I3, a solenoid I1 for operating the solenoid controlled valve I1 in the refrigerant supply line |4, and a compressor motor 39 for the condensing unit to the source of electrical energy S are also closed by the thermostat 24 during the refrigerating cycle.

The circuits connecting the solenoid |1' and the compressor motor 39 to the source of energy S also include a refrigerator thermostat of the usual type 4U that controls the operation of the compressor motor 39 and the valve I1 in the supply line in accordance with the temperature requirements of the refrigerator. The solenoid |1' is arranged to open the valve I1 in the supply line when it is energized so that the valve I1 will be closed when the circuit to its control solenoid |1 is interrupted by the operation of either the differential thermostat 24 or the refrigerator thermostat 40. v

Upon the start of and during a defrost cycle, the operation of the differential thernflostat 24 4 connects a solenoid 29' for operating the solenoid controlled valve 29 in the defrost line 28 to the vsource of electrical energy S. The solenoid 29 frigerating cycle. The rate at which the heating of the liquid 2| takes place may be varied by adjusting the rheostat 31 and in addition, the temperatures at which the differential thermostat 24 operates may be adjusted within limits as desired or a thermostat 24 may be selected with appropriate operating characteristics. The thermostat 24 may be set, for example, to open the circuit to the heater 23 when the temperature of the defrost liquid 2| reaches 130 F. and to close the heater circuit When the temperature of the liquid 2| drops to F. And the rheostat 31 may be set so that the heating of the liquid 2| from 120 F. to F. by the heater 23 Will take eight hours if that is the length of the refrigeration cycle desired.

At the start of a defrost cycle, a small amount of liquid refrigerant is contained in the evaporator II and in the refrigerant collector 39. When the valve 29 in the defrost line 28 is opened this liquid refrigerant flows under gravity through the defrost lines 28 and 21 to the heat exchanger 22 Where, due to the high temperature of the liquid 2| in the unit |9, the liquid refrigerant is vaporized. The liquid head of the liquid refrigerant flowing to the heat exchanger 22 causes the hot refrigerant gas resulting from the vaporizing of the liquid refrigerant to flow through the line 26, the suction line I5 to the evaporator coil I I and through the line 33 to the defrost coil 32 thus providing a simultaneous defrosting of the evaporator and of any ice collected in drain pan 34.

The cold surfaces of the evaporator II and the drain pan 34 cause the hot refrigerant gas to cool and condense as it flows through the evaporator coil and the defrost coil 32, thus, imparting its latent heat to such ice covered surfaces of the evaporator coil and the drain pan which causes the ice to melt and drain from the cooling unit. The condensed refrigerant liquid is continuously being revaporized and recycled as it flows by gravity through the defrost lines 28, 3| and 21 back to the heat exchanger 22 in the unit I9 Where it is reheated and vaporized. The defrost drain line 3| from the coil 32 under false drain pan 34 extends inside of the water drain line 36 to a point outside of the refrigerator so that ice Will not form in the drain line 36 during the defrost cycle. While the defrosting operation is being carried on the liquid 2| in the unit |9 cools and when it has cooled to a point where the differential thermostat 24 operates to close the circuit to the heater 23, the circuits to the refrigerating apparatus are also re-established in the manner previously described and the refrigerating cycle is started. The throttling valve IB in the suction line I5 limits the suction that may be pulled through the suction line and prevents an overload on the compressor motor 39 at the start of the refrigerating cycle due to pressures that are built up in the system during the defrosting operation.

Fromthe foregoingit willbe seen 'that the de-` frosting operation is completely automatic'and is entirely independent of the condensing unitso that the defrosting .capacity is vnot limited by the amount of hot gas that can bepumped by the compressor. Also, the compressor is shut. down during the defrosting cycle, thus conserving power.

The defrosting capacity,` expressed in heat units, depends on the .amountthe .liquid 2l in the defrosting unit is allowed to cool before the refrigerator cycle is repeated. This is controlled by the differential setting of the thermostat 24 and isadjustable over awide range. Obviously, this can also be varied if necessary by selecting a suitable thermostat for the temperature range desired. The duration of the defrost cycle also depends on Athe differential setting ofthe thermostat. The speed of the defrostingdepends upon the temperature to whichthe liquid 2I in the unit I9 for defrosting the evaporator coil is heated and this is controlled by the temperature setting of the thermostat 24, which is also adjustable over a wide range.

It Will, thus, -be seen thatthe temperature, the temperature range and the rate of temperature change of the liquid in the unit I9 for defrosting the evaporator coil are utilized in conjunction with the controls to regulate and automatically control the defrosting capacity and the duration of both the defrosting and refrigerating cycles and to provide adjustable means for varying both the capacity and duration of these cycles.

If desired, the duration of the refrigeration cycle and the defrosting cycle may be controlled by a conventional timing `device thatV will initiate the respective cycles at predetermined time intervals. In this case, the thermostat 24 in the liquid 2| of the defrost unit I9 maybe connected directly to the immersion heater 23 to control the heating of the liquid and will not control the operation of the valves I'i and 29. In this case the rheostat controlling the rate of heating may also be eliminated. Also, the solenoid controlled valves I'I and 29 may be provided with manual operating stems so that the cooling unit may be manually defrosted if desired.

In addition, a solenoid controlled valve may be located in the line 2f6 connecting the heat exchanger 22 to the suction line l5 if itis desired to shut the heat exchanger olf from the suction line. Such a valve will also be controlled by the operation of the differential thermostat 211,' or, if desired, the solenoid controlled valve 2-'9 in the defrost line 28v may be placed in the line 2S.

It will also be understood any suitable source of heat such as gas, electricity, steam or the like may be utilized for heating the liquid 2| in the defrosting unit. For example, in a refrigerated truck, the heat from the exhaust gases of the engine that is ordinarily wasted may be utilized for this purpose.

It will be understood that various modifications and variations particularly Yas -to types of material, controls, arrangement of the apparatus 'and construction may be made in the `embodiment of the invention as described illustra-ted herein without departing from the yscope ofthe inventionias denediby 'the appended claims.

I claim:

l. -An apparatus for automatically defrosting a refrigeratorA wherein het refrigerant gas-is -heated and circulated through an evaporator independently of the refrigerator condensing unit comprising thecom-bination ofl-anvevaporator, said evaporator having a suctionline andrefrigerant supply line connected to a condensing unit, .a chamber containing a xed quanity of a liquid, a heat exchanger submerged in said liquid, said heat exchanger being connected to the evaporator, an electrically operable valve located in the connections between the evaporator .and the heat exchanger for controlling the iiow of refrigerant through the heat exchanger, a second electrically operable valve located in the refrigerant supply line to the evaporator for controlling the supply of liquid refrigerant from the condensing unit to the evaporator, a differential thermostat operable by the temperature of the liquid in said chamber, circuits controlled by the operation of said thermostat for operating the valves in the connections to the defrosting unit and in the refrigerant supply line upon the temperature of saidliquid reaching predetermined values and a heater for heating the liquid in said chamber, said heater being independent of the refriger ator condensing unit and controlled by the operation of the thermostat.

2. An apparatus for automatically defrosting an evaporator for a refrigerator as defined in claim l including a collector for collecting liquid refrigerant connected between the evaporator and the heat exchanger.

3. An apparatus for automatically defrosting an evaporator for a refrigerator as defined in claim 1 including a defrosting coil connected to the `heat exchanger and located beneath the evaporator.

4. An apparatus for automatically defrosting an evaporator for a refrigerator as defined in claim 1 including a collector for collecting liquid refrigerant connected .between the evaporator and the heat exchanger and a defrosting coil con-v nected to the heat exchanger and located beneath the-evaporator..

5,. An apparatus for automatically defrosting an evaporator of a refrigerator by periodically circulating hot refrigerant gas through the evapv orator independently of a condensing unit for the evaporator comprising the combination of a chamber containing a'xed quantity o f a liquid, a heat exchanger located submerged in said liquid, a heater for heating said liquid, a collector connected to and located beneath the evaporator for collecting liquid refrigerant from the evaporator, a `valve-controlled connection from the .collector to the heat exchanger, said connection when open permitting liquid refrigerant to flow from the collector and the evaporator to the Yheat ,4 exchanger whereby the liquid refrigerant flowing Athe temperature of the liquid in the defrosting unit reaches predetermined values.

6. In an apparatus for defrosting an evaporator for a refrigerator by circulating hot refrigerant gases through the Yevaporator' independently of its condensing unit comprising the combination of a chamber containing a xed quantity of a liquid, a heat exchanger submerged in the 1iquid,a heater for heating said liquid to a predetermined temperature, a collector connected to and located beneath the evaporator for collecting liquid refrigerant from the evaporator, a valve-controlled connection from the collector to the heat exchanger, said connection when open permitting liquid refrigerant to flow from the co1- lector to the heat exchanger, and a connection from the heat exchanger to the evaporator for permitting hot refrigerant gas resulting from the heating and vaporizing of the liquid refrigerant in the heat exchanger to flow from the heat exchanger to the evaporator.

7. An apparatus as defined in claim 6 including a thermostat operable by the temperature of the liquid in said chamber and a circuit controlled by said thermostat for controlling the operation of the heater for heating the liquid.

8. The method of defrosting an evaporator of a refrigeration unit in which hot refrigerant gas is circulated through the evaporator independently of a condensing unit for the evaporator, which comprises the steps of heating a xed quantity of a liquid at a constant rate to a predetermined temperature in a zone insulated from the refrigeration unit, said heating being carried out independently of the condensing unit during a refrigerating cycle of the evaporator, then heating and vaporizing a liquid refrigerant from the evaporator in said heated liquid and then circulating the vaporized refrigerant resulting from said heating of the liquid refrigerant through the evaporator, said heating and circulating steps being carried out with the connections between the evaporator and the condensing unit closed.

9. The method of defrosting an evaporator of a refrigeration unit in which hot refrigerant gas is circulated through the evaporator independently of a condensing unit for the evaporator, which comprises the steps of heating a fixed quantity of a liquid at a constant rate to a temperature in the neighborhood of 130 F. in a zone insulated from the refrigeration unit, said heating being carried out independently of the' condensing unit during a refrigerating cycle of the evaporator, then heating and vaporizing a liquid refrigerant from the evaporator in said heated liquid and then circulating the vaporized refrigerant resulting from said heating of the liquid refrigerant through the evaporator, said heating and circulating steps being carried out with the connections between the evaporator and the condensing unit closed.

10. The method of defrosting an evaporator of a refrigeration unit in which hot refrigerant gas is circulated through the evaporator independently of a condensing unit for the evaporator, which comprises the steps of heating a xed quantity of a liquid at a constant rate to a predetermined temperature in a zone insulated from the refrigeration unit, said heating being carried out independently of the condensing unit during a refrigerating cycle of the evaporator, then heating and vaporizing a liquid refrigerant from the evaporator in said heated liquid and then circulating the vaporized refrigerant resulting from said heating of the liquid refrigerant through the evaporator under the head of the liquid refrigerant in the evaporator, said heating and circulating steps being carried out with the connections between the evaporator and the condensing unit closed. y

11. The method of automatically defrosting ank evaporator of a refrigeration Yunit periodically wherein a liquid refrigerant is heated and hot refrigerant gas is circulated through the evaporator independently of a condensing unit for the evaporator, which comprises the steps of heating a fixed quantity of a liquid independently of a. condensing unit for an evaporator in a zone insulated from the evaporator, said heating being conducted during the refrigeration cycle of the evaporator and at a constant rate, stopping the operation of the condensing unit upon the temperature of said liquid reaching a predetermined value, then heating the liquid refrigerant from the .evaporator in said heated liquid and vaporizing the same and then circulating the vaporized refrigerant resulting from said heating of the liquid refrigerant through the evaporator.

f 12. The method of periodically and automatically defrosting an evaporator of a refrigeration unit where a liquid refrigerant is heated and hot refrigerant gas is circulated through the evaporator independently of a condensing unit for the evaporator, which comprises the steps of heating a fixed quantity of a liquid independently of a condensing unit for an evaporator in a zone insulated from the evaporator, said heating being conducted during the refrigeration cycle of the evaporator and at a constant rate, stopping the operation of the condensing unit upon the temperature of said liquid reaching a predetermined value and then heating the liquid refrigerant from the evaporator in said heated liquid and vaporizing the same and then circulating the vaporized refrigerant resulting from the heating of the liquid refrigerant through the evaporator under the head of the liquid refrigerant in the evaporator.

13. In a system for defrosting an evaporator of a refrigeration unit wherein hot refrigerant gases are circulated through the evaporator independently of a condensing unit for the evaporator, the combination which includes a chamber containing a xed quantity of a liquid, said chamber being insulated from the evaporator, means for heating the liquid in said chamber at a constant rate, said heating means being independent of the condensing unit for the evaporator, a heat exchanger in said heated liquid, said heat exchanger being connected to the evaporator, a valve located in one of the connections between the heat exchanger and the evaporator, said valve normally being closed during a refrigerating cycle of the evaporator and means for opening said valve, the operation of said valve-opening means being controlled by the temperature of the heated liquid.

14. In a system for defrosting an evaporator of a refrigeration unit wherein hot refrigerant gases are circulated through the evaporator independently of a condensing unit for the evaporator, the combination as defined in claim 13 wherein the means for heating the liquid at a constant rate is adjustable.

15. In a system for defrosting an evaporator of a refrigeration unit wherein hot refrigerant gases are circulated through the evaporator independently of a condensing unit for the evaporator, the combination which includes a chamber containing a fixed quantity of a liquid, said chamber being insulated from the evaporator, means for heating the liquid in said chamber at a constant rate, said heating means being independent of the condensing unit for the evaporator, a heat exchanger in said heated liquid, said heat exchanger being connected to the evap- 10 orator, a valve located in one of the connections between the heat exchanger and lche evaporator, REFERENCES CITED Said Valve normally beng closed during a reg-121g' The following references are of record in the erating cycle of the evaporator, a second :vafve me of this patent: located in a supply lnenconnectng the evapopa- 5 tor to the condensing unit, said second valve nor- UNTTED STATES PATENTS mally being open during'` the refrigerating'cygle and means for opening the rst valve and'clos- 121351233 Leeslggme Nov Dt-'(21947 ing the second valve, theoperation of said `valve 2430'960 501mg Noiv 18' 1947 opening and closing means being controlled-@by 1o 2'449146 Kramm? Abi' 20' 1948 the temperature of the neated liquid. 2:452102 Cocanour O-'t' 26' 1948 THOMAS L. 

